Compliant seals for preventing gas leakage between a stationary housing and a rotating shaft passing therethrough are well known. Such seals include a plurality of individual bristles consisting of metallic wire or other fiber, extending from a backing member into contact with the rotating shaft. The ends of the bristles brush lightly against the rotating shaft, hence such seals may also be termed "brush seals".
The packed bristles of the seal discourage gas flow between the stationary housing and the shaft, while the contact of the bristles with the shaft establishes a "zero clearance" between the seal and shaft further enhancing the seal effectiveness.
Such seals include inherent advantages in terms of resistance to high temperatures and the ability to accommodate radial runout of the shaft, as well as reduced component cost as compared to known labyrinth or knife edge seals used in gas turbine engines.
As has long been appreciated by those familiar with such sealing elements, it is necessary to pack the individual bristles uniformly about the circumference of an annular seal as well as to align each bristle element properly so as to achieve the desired advantages. It is easily apparent that even a slight deficiency in the arrangement of the bristles about the backing ring can give rise to a leakage path which could compromise the brush seal effectiveness.
Present methods of manufacturing brush seals preassemble a quantity of individual bristles into a quantity of small bundles which are arranged and temporarily secured at the desired alignment. The backing member is fabricated from two annular rings which are disposed on opposite sides of the assembled bristle bundles with the bristles and annular backing rings being permanently secured, thus forming the completed seal.
One such method, disclosed in U.S. Reissue Pat. No. 30,206, provides an annular holding ring having a plurality of radial holes disposed therein. Bundles of individual bristles are drawn radially into the holes and secured by a wire loop pulled manually through the holding ring outer periphery. After drawing all the individual bristle bundles into the holding ring, first and second annular backing rings are fused to the bristles and the brush seal separated from the holding ring by cutting or otherwise machining away the excess bristle material. The remainder of the individual bristle bundles must then be removed from the holding ring and the process repeated for the next seal.
Another prior art method, disclosed in U.S. Pat. No. 4,274,575, preassembles individual bristle bundles into short cylindrical tubes, arranging a plurality of such tubes about an annular holding member in the desired orientation. The small tubes may be secured by adhesive or some other convenient scheme. The annular backing rings are again placed adjacent the protruding bristles and fused or otherwise permanently secured to form the brush seal.
Such preassembly methods require additional steps to temporarily secure the individual bristle bundles prior to positioning and permanently securing the annular backing rings. Additionally, the use of discrete bundles of bristles can result in a nonuniformity of the bristle density in the circumferential direction. Further, and in particular with respect to the holding member having a plurality of radial passages disposed therein, repeated use of the holding member results in wearing of the passages and the possibility of the occurrence of misalignment of individual bristles.
What is needed is a simple, effective method for temporarily positioning, aligning, and restraining individual bristles prior to permanently securing the bristles to the backing members.